Electrical bushing with resin casting

ABSTRACT

The invention in a first aspect relates to an improved cast resin bushing assembly for use in a transformer wherein the busing assembly includes a bushing which includes locating means for aligning the bushing assembly within a transformer casing; wherein the bushing further includes a locking means for releasably securing the bushing assembly to a transformer casing; a bushing conductor; and a bushing flange in circumferential arrangement with the bushing. In a second aspect the invention relates to a method of securing an improved cast resin bushing assembly to a transformer casing which bushing assembly includes a bushing which includes a locating means for aligning the bushing assembly within a transformer casing; the bushing further includes a locking means for releasably securing the bushing assembly to a transformer casing; a bushing conductor, and a bushing flange in circumferential arrangement to the bushing; wherein the transformer casing has an opening adapted to receive the bushing assembly or part thereof; and the bushing flange is mounted on the outside of the transformer casing and secured thereto by engaging the locking means on the inside of the transformer casing.

This application is a continuation of international application numberPCT/AU00/00204, filed March 17, 2000 which claims the benefit ofpriority from Australian Patent Application No. PP9218 filed Mar. 17,1999.

FIELD OF THE INVENTION

The invention relates to improved electrical bushings with resincasting. In particular the invention relates to advances in the use ofcast resin systems which enables improved fixing and sealing of anelectrical bushing insulator to a transformer case.

BACKGROUND OF THE INVENTION

Typically a grid of power lines distributes electricity from either thepoint of generation or substations throughout both metropolitan andrural areas. Power is normally distributed at 11-36KV from the point ofgeneration or from substations. In order to effectively supply power(electricity) for domestic use in home or business, transformers areemployed at substations so as to step down the voltage to lower levelsfor subsequent conducting through a distribution network. Suchtransformers typically supply domestic users with between 110 to 450 Vof electricity. Therefore transformers are subject to high inputvoltages and lower output voltages which supply a subsequent powerdistribution network.

The transformer requires insulative conductors on both the high and lowvoltage sides to protect the transformer from shorting to the Earth. Thetransformer case is usually metal and must be safely insulated.Electrical bushings provide a safe means of passing electrical currentthrough the transformer casing. Normally an electrical conductor issealed within such an electrical bushing so as to prevent leakagebetween the bushing and the conductor and to present electricalterminals extending from the interior of the transformer tank.

Electrical bushings of the prior art are produced in a variety ofconfigurations so that they can be permanently affixed upon anelectrical transformer by a welding process or the like. The bushingpresents an electrical conductor through an opening in the wall of atransformer into the interior thereof which is filled with transformeroil or inert gas. Conventional bushings are provided with an insulativecomponent and an exterior mounting flange affixed upon the component,which flange is adapted to be welded upon the transformer tank in orderto permanently fix the bushing to the transformer in a way which sealsthe opening therein. It is a requirement that the bushing provides amechanical seal, air to air, air to gas, or air to oil, dependent on thetransformer design.

In the prior art, bushings welded upon a transformer suffer thedisadvantage of sacrificing the ability of the bushing or transformer tobe easily repaired or replaced. It is a frequent occurrence, due toaccident or malfunction, that the bushing requires repair orreplacement, however because the bushing can't be easily removed withoutextensive labour, complete replacement of the transformer is often theend result.

Further disadvantages of the prior art such as oil leakage, may occurbecause the welding process to seal the bushing into the transformer maynot form a complete seal, it is often the case that such leakage willnot be detected until final stages of manufacture when correctivemeasures are costly.

Generally the prior art can be regarded in two categories—ceramic andnon-ceramic. Ceramic prior art has been limited in design due to thematerials employed. For example porcelain bushings cannot be cast inasymmetrical shapes. Also, the difference in expansion coefficientbetween the conductor and the insulator means that the conductor cannever be cast into the bushing. This limitation complicates both theassembly of the unit as a whole, the fixing of the bushing to thetransformer and also the sealing of the bushing unit.

It is desirable for a bushing to be able to be held in angular relationto a transformer casing. This angular configuration is usually achievedby providing a modified transformer casing with a gusset upon which aporcelain bushing is seated. Transformer casings which are modified toinclude a gusset are expensive and time consuming to construct. Priorart porcelain bushings and assemblies have so far been unable to meetthis desire.

Non Ceramic prior art addresses some of these shortcomings, for examplethe casting of the conductor into the resin system, but does notadequately address the fixing of the bushing to the transformer andsealing of the bushing to the transformer case. Prior art has alsoexplored various metallic clamping devices on the inside or outside ofthe transformer, all of which detract from the insulative capacity ofthe bushing.

SUMMARY OF THE INVENTION

Against the foregoing background, it is an object of the presentinvention to overcome the disadvantages of the prior art.

It is a further object of the invention to provide an improved bushingwhich advances the use of cast resin systems for a bushing design.

A further object of the invention is to provide an improved bushingassembly which greatly improves and facilitates the fixing and sealingof the bushing to a transformer case. In particular the new improvedbushing serves to effectively provide a mechanical seal therebypreventing any leakage, but at the same time enables easy removal of thebushing so that a transformer doesn't have to be fully replaced.

The invention in a first aspect relates to an improved cast resinbushing assembly for use in a transformer wherein the bushing assemblycomprises:

a bushing which bushing includes locating means for aligning the bushingassembly or part thereof within an opening in a transformer casing;

wherein the bushing further includes a locking means for releasablysecuring the bushing assembly to a transformer casing;

a bushing conductor integrally moulded to said bushing; and

a bushing flange in circumferential arrangement with the bushing.

In a second aspect the invention relates to a method of securing animproved cast resin bushing assembly to a transformer casing whichbushing assembly comprises:

a bushing which bushing includes a locating means for aligning thebushing assembly or part thereof within an opening in a transformercasing;

the bushing further includes a locking means for releasably securing thebushing assembly to a transformer casing;

a bushing conductor integrally moulded to said bushing; and

a bushing flange in circumferential arrangement to the bushing;

positioning said locating means on said bushing within said transformeropening so as to align said bushing assembly;

mounting said bushing flange on an outside surface surrounding thetransformer opening;

releasably securing the bushing assembly within the transformer casingby engaging said locking means inside the transformer casing.

PREFERRED ASPECTS OF THE INVENTION

Preferably the locking means is a threaded section moulded into thebushing adapted to be engaged by a corresponding collar inside atransformer casing.

Preferably the threaded section and the collar are cast in the samemould.

Preferably the collar can be a cast resin nut.

Preferably the locating means comprises a groove or flat portion foraligning the bushing assembly within an opening in a transformer casing.

Preferably the bushing flange is adapted to be mounted on a transformercasing.

Preferably the bushing flange has up to four locating holes foradditional securement to a transformer casing.

Preferably the bushing conductor is cast within the bushing.

Preferably the bushing assembly is cast in a one step mould process.

In one embodiment of the invention there is disclosed a method ofreleasably securing an improved cast resin bushing assembly to atransformer casing by providing a bushing assembly including:

a bushing which bushing includes a groove or flat portion for aligningthe bushing assembly or part thereof within an opening in thetransformer casing;

the bushing further includes a threaded section for securing the bushingassembly to the transformer casing;

a threaded collar;

a bushing conductor integrally moulded to said bushing; and

a bushing flange in circumferential arrangement with the bushing;

positioning said locating means on said bushing within said transformeropening so as to align said bushing assembly;

mounting said bushing flange on an outside surface surrounding thetransformer opening;

releasably securing the bushing assembly within the transformer casingby engaging the threaded section on the bushing on the inside of thetransformer casing with the threaded collar.

In a further specific embodiment it is preferred that the collar is acyclo nut. In yet a further preferred embodiment the bushing flangeincludes locking holes which can be used as an additional or alternatemeans of securing the bushing assembly to the transformer casing wherebystuds or nuts are lockably engaged to secure the bushing flange againstthe transformer casing.

Preferably the cast resin system is selected from Epoxy, Phenolic,Polyester, Vinyl Ester, Polyurethane and related composites. Morepreferably the cast resin system is a cycloaliphatic Epoxy Resin System.

Preferably the bushing assembly is cast in asymmetric or symmetricdesign.

Preferably the improved bushing assembly further comprises a flangemoulded to the bushing wherein the flange is substantially annular andhas an outside diameter larger than the transformer opening.

Preferably the threaded section of the bushing is cast in a resinmoulding together with a complementary nut or collar.

In use customers have a choice as to which arrangement best suits theirpurpose. In some instances for example in subterranean applications thethreaded cast resin section and nut or collar are preferred because theuse of studs in this application may be a point of potential corrosioninitiation.

BRIEF DESCRIPTION OF THE VIEW OF THE DRAWINGS

FIG. 1 is a perspective view of the improved bushing assembly.

FIG. 2 is an enlarged cross-sectional view of a bushing assemblyconnected to a transformer casing.

FIG. 3 is an elevated view in cross section.

FIG. 4 is a plan view of a transformer showing a threaded section heldin place by a matching collar.

FIG. 5 is a reduced plan view of FIG. 2.

FIG. 6A is an elevational view of one embodiment of a electrical bushingconstructed according to the teachings of the present invention;

FIG. 6B is an elevational view of another embodiment of an electricalbushing constructed according to the teachings of the present invention;

FIG. 6C is a plan view of a gasket for being received over a cylindricalpart with a flat;

FIG. 7A is a side elevational view of an electrical bushing constructedaccording to the teachings of the present invention with portions brokenaway and with portions shown in section to show the assembly of a nut onthe bushing;

FIG. 7B is a plan view of the nut; and

FIG. 7C is a plan view of a gasket for being received over a cylindricalpart with a flat.

INTEGER LIST

-   1. Locating means-   5. Transformer lid-   6. Gasket-   7. Flange-   8. Washer-   9. Nut-   10. Bolt-   11. Bushing-   12. Nut or collar-   13. Cast threaded section-   15. Conductor-   16. Transformer casing-   17. Cast resin moulded section-   18. Moulded openings

DETAILED DESCRIPTION WITH RESPECT TO THE DRAWINGS

As previously noted, this invention relates to an improved electricalbushing assembly which facilitates fixing and sealing of a bushing to atransformer case but which does not detract from the insulative capacityof the bushing.

Referring now to the drawings, there is shown in one embodiment of theinvention a bushing assembly adapted to be received within an openingwhich comprises either one of two types of locking means for releasablysealing a bushing 11 to a transformer casing 16. The bushing assemblycomprises a cast resin moulded section 17 which section includes aflange 7 adapted to be mounted on a transformer lid 5, a bushing 11 andbushing conductor 15 integrally moulded thereto. The bushing assemblyshows a threaded section 13 immediately below the flange (7) adapted tobe engaged by a nut or collar 12 inside the transformer casing (16).There is also shown a flattened or grooved section 1 on the bushing 11so as to enable alignment of the bushing in the transformer casing.

In general the bushing assembly 17 is adapted to be received within anopening in a transformer casing 16 and the bushing flange 7 is adaptedto be mounted or secured on the transformer casing. It is understoodthat a part of the bushing assembly is exposed to air while another partthereof, housed within the transformer casing is exposed to an oilenvironment.

In the embodiment described by FIG. 2 there is shown two types oflocking means. In a first type, the bushing 11 can be fixed and sealedin position by means of passing bolts 10 located on the transformer lid5 through moulded openings in the flange 7 wherein a nut 9 is disposedon the bolt and tightened thereof. In order to provide an air tight sealthe nut 9 is screwed down against a washer 8 disposed between the nutand the flange and the flange is urged against a gasket 6 to form a sealwith the transformer lid.

In a second type there is shown a cast resin threaded section 13 whichis integrally moulded with the bushing 11. The threaded section 13 isdisposed internally of the transformer casing 16 while the bushingflange 7 is mounted on transformer lid 5 and the bushing 11 is securelyfixed and sealed in position by tightening a collar 12 about thethreaded section 13. The collar 12 may be cast from the same resinsystem as the threaded section 13 or indeed even the same mould so thatthe threaded section and collar compliment the insulative value of thebushing. In this respect the prior art has explored various metallicclamping devices on the inside or outside of the transformer all ofwhich detract from the insulative capacity of the bushing.

In a further preferred embodiment of the invention in FIG. 4 there isshown a bushing assembly secured to a transformer casing which bushingassembly is of the second type as described previously employing a castresin threaded section. It is noted in this embodiment referring to FIG.4 that points of potential corrosion created by the use of bolts weldedto the transformer lid are avoided.

In each of the embodiments it is understood that not only do thedifferent bushing assemblies mechanically fix and seal the bushingwithin the transformer but they enable easy removal and replacement ofcomponent parts so as to obviate the need to completely replace atransformer.

In yet a further embodiment of the invention shown in FIGS. 6 and 7, thebushing assembly is held in angular relation to the transformer casing.

It is desirable for a bushing to be able to be held in angular relationto a transformer casing. This angular configuration is usually achievedby providing a modified transformer casing with a gusset upon which aporcelain bushing is seated. Transformer casings which are modified toinclude a gusset are expensive and time consuming to construct. Priorart porcelain bushings and assemblies have so far been unable to meetthis desire.

The present applicants cast resin bushing assembly can be cast in anangular or bifurcated configuration so as to locate within a transformercasing at an angle and accommodate a conventional transformer casing. Inthis way transformer casings need not be modified to accommodate priorart porcelain bushings in angular relation.

In this preferred embodiment the bushing can be located at an angle ofup to at least 50° to the transformer casing.

The claims, illustrations, photographs and drawings, if any, form partof the disclosure of this specification as does the description, claims,illustrations, photographs and drawings of any associated provisional orparent specification or of any priority document, if any, all of whichare imported hereinto as part of the record hereof.

Finally it is to be understood that various alterations, modificationsand/or additions may be incorporated into the various constructions andarrangements of parts without departing from the spirit and admit of theinvention.

1. An improved cast resin busing assembly for use in a transformerincluding: a bushing which includes locating means for aligning thebushing assembly within a transformer casing; said busing furthercomprising locking means for releasably securing the bushing assembly tosaid transformer casing; said locking means including a threaded sectionmoulded into the bushing that is adapted to be engaged by a collarinside said transformer casing; a bushing conductor integrally mouldedto said bushing; and a bushing flange in circumferential arrangementwith the bushing.
 2. An improved cast resin bushing assembly accordingto claim 1 wherein the bushing assembly is cast in a one step moulding.3. An improved cast resin bushing assembly according to claim 1 whereinthe threaded section of the bushing and the collar are cast from asingular resin moulding so as to form complementary engageablecomponents.
 4. An improved cast resin bushing assembly according toclaim 1 wherein the locating means is a groove or flat position on thebushing for aligning the bushing assembly within an opening in saidtransformer casing.
 5. An improved cast resin bushing assembly accordingto claim 1 wherein the bushing flange is adapted to be mounted on saidtransformer casing.
 6. An improved cast resin bushing assembly accordingto claim 1 wherein the bushing flange includes locking holes which canbe used as additional alternate means of securing the bushing assemblyto the transformer casing.
 7. An improved cast resin bushing assemblyaccording to claim 1 wherein the bushing flange and the bushingconstitute a single moulded piece.
 8. An improved cast resin bushingassembly according to claim 1 wherein the flange is substantiallyannular and has an outside diameter larger than the transformer opening.9. An improved cast resin bushing assembly according to claim 1 whereinthe bushing conductor is cast integrally within the bushing.
 10. Animproved cast resin bushing assembly according to claim 1 wherein thecast resin system is selected from epoxy, phenolics, polyester,vinylester, polyurethane and related composites.
 11. An improved castresin bushing assembly according to claim 1 wherein the collar can be acast resin nut or cyclo nut.
 12. A method of releasably securing animproved cast resin bushing assembly to a transformer casing having anopening by providing: a bushing which includes locating means foraligning the bushing assembly or part thereof within said opening insaid transformer casing; the bushing further includes locking means forreleasably securing the bushing assembly to said transformer casing; thelocking means including a threaded section moulded into the bushingwhich is adapted to be engaged by a collar inside said transformercasing; a bushing conductor integrally moulded to said bushing; and abushing flange in circumferential arrangement to the bushing; saidmethod including the steps of: positioning said locating means on saidbushing within said opening in said transformer casing so as to alignsaid bushing assembly; mounting said bushing flange on an outsidesurface surrounding the opening in said transformer casing; and,releasably securing the bushing assembly within the transformer casingby engaging said locking means inside the transformer casing.
 13. Amethod of releasably securing an improved cast resin bushing assembly toa transformer casing according to claim 12 wherein the bushing assemblyis cast in a one step moulding.
 14. A method according to claim 12wherein the threaded section of the bushing and the collar are cast froma singular resin moulding so as to form complementary engageablecomponents.
 15. A method according to claim 12 wherein the collar can bea cast resin nut or cyclo nut.
 16. A method according to claim 12wherein the locating means is a groove or flat position on the bushingfor aligning the bushing assembly within an opening in said transformercasing.
 17. A method according to claim 12 wherein the bushing flange isadapted to be mounted on said transformer casing.
 18. A method accordingto claim 12 wherein the bushing flange includes locking holes which canbe used as additional or alternate means of securing the bushingassembly to the transformer casing.
 19. A method according to claim 12wherein the bushing flange and the bushing constitute a single mouldedpiece.
 20. A method according to claim 12 wherein the flange issubstantially annular and has an outside diameter larger than thetransformer opening.
 21. A method according to claim 12 the bushingconductor is cast integrally within the bushing.
 22. A method accordingto claim 12 wherein the cast resin system is selected from epoxy,phenolics, polyester, vinylester, polyurethane and related composites.23. A method of releasably securing an improved cast resin bushingassembly to a transformer casing having an opening by providing abushing assembly including: a bushing which is formed from a cast resinpolymer and which includes locating means defined by one of a groove orflat portion for aligning the bushing assembly or part thereof withinsaid opening in the transformer casing; the bushing further includes athreaded section for securing the bushing assembly to the transformercasing; a threaded collar; a bushing conductor integrally moulded tosaid bushing; and a bushing flange in circumferential arrangement withthe bushing; said method includes the steps of: positioning saidlocating means on said bushing within said opening in said transformercasing so as to align said bushing assembly; mounting said bushingflange on an outside surface surrounding said opening in saidtransformer casing; and, releasably securing the bushing assembly withinthe transformer casing by engaging the threaded section on the bushingon the inside of the transformer casing with the threaded collar.
 24. Animproved cast resin bushing assembly for use in a transformer including:a bushing which is made from a cast resin polymer, which is cast inangular or bifurcated construction relative to a transformer casing andwhich includes located means for aligning the bushing assembly withinthe transformer casing; said busing further comprising locking means forreleasably securing the bushing assembly to said transformer casing; abushing conductor integrally moulded to said bushing; and a bushingflange in circumferential arrangement with the bushing.
 25. An improvedcast resin bushing assembly for use in a transformer including: abushing which includes locating means for aligning the bushing assemblywithin a transformer casing; said bushing being cast from acycloaliphatic epoxy resin system; said busing further comprisinglocking means for releasably securing the bushing assembly to saidtransformer casing; a bushing conductor integrally moulded to saidbushing; a bushing flange in circumferential arrangement with thebushing.
 26. A method of releasably securing an improved cast resinbushing assembly to a transformer casing having an opening by providing:a bushing which includes a locating means for aligning the bushingassembly or part thereof within said opening in said transformer casing;the bushing further includes a locking means for releasably securing thebushing assembly to said transformer casing; a bushing conductorintegrally moulded to said bushing; and a bushing flange incircumferential arrangement to the bushing; positioning said locatingmeans on said bushing within said opening in said transformer casing soas to align said bushing assembly; and said method comprising the stepsof: casting said bushing from a cycloaliphatic epoxy resin system;mounting said bushing flange on an outside surface surrounding theopening in said transformer casing; and, releasably securing the bushingassembly within the transformer casing by engaging said locking meansinside the transformer casing.